Localization and "classical entanglement'' in the Discrete Non-Linear Schrödinger Equation

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Main Authors: Giachello, Martina, Iubini, Stefano, Livi, Roberto, Gradenigo, Giacomo
Format: Preprint
Published: 2025
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author Giachello, Martina
Iubini, Stefano
Livi, Roberto
Gradenigo, Giacomo
author_facet Giachello, Martina
Iubini, Stefano
Livi, Roberto
Gradenigo, Giacomo
contents We perform a detailed numerical study of the very peculiar thermodynamic properties of the localized high-energy phase of the Discrete Non-Linear Schrödinger Equation (DNLSE). A numerical sampling of the microcanonical ensemble done by means of Hamiltonian dynamics reveals a new and subtle relation between the presence of the localized phase and a property of the system that we have called {\it ``classical entanglement''}. Our main finding is that a quantity defined for our classical system in perfect analogy with the entanglement entropy of quantum ones, and that we have therefore called $S_{\mathrm{ent}}$, grows with the system size $N$ in the localized phase as $S_{\mathrm{ent}}(N) \sim \log(N)$, therefore revealing the presence of subtle non-local correlations between any finite portion of the system and the rest of it. This manifestation of {\it ``classical entanglement''} beautifully captures the lack of system separability in the DNLSE localized phase, revealing how statistical correlations specific to the microcanonical ensemble and non-reproducible in the canonical one, may concur to determine a property totally analogous to the one produced by non-local quantum correlations.
format Preprint
id arxiv_https___arxiv_org_abs_2503_14364
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Localization and "classical entanglement'' in the Discrete Non-Linear Schrödinger Equation
Giachello, Martina
Iubini, Stefano
Livi, Roberto
Gradenigo, Giacomo
Statistical Mechanics
Quantum Physics
We perform a detailed numerical study of the very peculiar thermodynamic properties of the localized high-energy phase of the Discrete Non-Linear Schrödinger Equation (DNLSE). A numerical sampling of the microcanonical ensemble done by means of Hamiltonian dynamics reveals a new and subtle relation between the presence of the localized phase and a property of the system that we have called {\it ``classical entanglement''}. Our main finding is that a quantity defined for our classical system in perfect analogy with the entanglement entropy of quantum ones, and that we have therefore called $S_{\mathrm{ent}}$, grows with the system size $N$ in the localized phase as $S_{\mathrm{ent}}(N) \sim \log(N)$, therefore revealing the presence of subtle non-local correlations between any finite portion of the system and the rest of it. This manifestation of {\it ``classical entanglement''} beautifully captures the lack of system separability in the DNLSE localized phase, revealing how statistical correlations specific to the microcanonical ensemble and non-reproducible in the canonical one, may concur to determine a property totally analogous to the one produced by non-local quantum correlations.
title Localization and "classical entanglement'' in the Discrete Non-Linear Schrödinger Equation
topic Statistical Mechanics
Quantum Physics
url https://arxiv.org/abs/2503.14364